Downhole pulser

ABSTRACT

A power generator for use in a wellbore formed in an earth formation, including an internal combustion engine having a cylinder and a piston defining a combustion chamber in the cylinder, the engine being arranged to induce a reciprocating movement to the piston relative to the cylinder upon combustion of a combustible gas mixture in the combustion chamber, and a linear electricity generator having a stator and a drive shaft. The generator is arranged to generate electricity upon a reciprocating movement of the drive shaft relative to the stator, and the piston is connected to the drive shaft so as to transmit the reciprocating movement of the piston to the drive shaft.

FIELD OF THE INVENTION

The present invention relates to a pulser for generating pressure pulsesin a wellbore formed in an earth formation.

BACKGROUND OF THE INVENTION

Hydrocarbon fluid is generally produced from an earth formation using awellbore provided with a casing or liner having perforations at thelevel of the producing formation. The hydrocarbon fluid flows throughthe pores of the earth formation and the perforations into the wellbore.

A problem frequently encountered during production is that the pores ofthe formation are naturally clogged by fine solids or diagenetic mineralparticles, or become clogged by fines solid particles in the course ofhydrocarbon fluid production, thereby decreasing the flow rate andincreasing the flow resistance. Another frequently encountered problemis that the perforations extending into the earth formation arecontaminated by crushed or fused rock particles as a result of the useof shaped explosive charges to create the perforations, or by residualmaterial from such shaped explosive charges. Such particles and residualmaterials impede the flow rate of hydrocarbon fluid.

It is an object of the invention to provided a device for reducing, oreliminating, the problem of reduced flow rate due to clogging of thepores of the earth formation.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a pulser forgenerating pressure pulses in a wellbore formed in an earth formation,comprising a housing provided with an internal combustion engineincluding a cylinder and a piston arranged to perform a combustionstroke upon combustion of a combustible gas mixture in the cylinder, afirst spring arranged to induce the piston to perform a compressionstroke upon completion of the combustion stroke, the pulser furthercomprising a hammer connected to the piston, an anvil movable relativeto the housing between a fist position and a second position in whichthe pulser has a different volume than in the first position, the anvilbeing arranged so that the hammer impacts against the anvil during thecombustion stroke and induces the anvil to move from the first to thesecond position, and a second spring biasing the anvil from the secondto the first position thereof.

By the impact of the hammer against the anvil during each combustionstroke, the anvil rapidly moves to the second position and therebycreates a pressure pulse in the fluid present in the wellbore by virtueof the sudden change of volume of the pulser. In this manner a sequenceof pressure pulses is generated, which pulses travel into the pores ofthe earth formation and thereby prevent settling of fine solid particlesin the pores.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in more detail and by way ofexample with reference to the accompanying drawings in which

FIG. 1 schematically shows an embodiment of the pulser according to theinvention;

FIG. 2 schematically shows in inlet valve of the embodiment of FIG. 1;and

FIG. 3 schematically shows an exhaust of the embodiment of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1 there is shown a pulser 1 for use in a wellbore (notshown) formed in an earth formation (not shown). The pulser 1 includes ahousing 2 provided with an internal combustion engine 4 and an anvil 6having a common longitudinal axis coinciding with, or parallel to, thelongitudinal axis of the wellbore.

The engine 4 comprises a cylinder 8 and a piston 10 extending into thecylinder 8 and being movable relative to the cylinder 8 in longitudinaldirection thereof. A hammer 12 connected to the piston 10 extends inlongitudinal direction to the anvil 6. The cylinder 8 is at the endthereof opposite the hammer 12 closed by an end wall 14, therebydefining a combustion chamber 16 formed in the cylinder 8 between thepiston 10 and the end wall 14. A compression spring 17 biased betweenthe piston 10 and an annular shoulder 18 of the cylinder 8, biases thepiston 10 to a retracted position in which the combustion chamber 16 hasa relatively small volume. The combustion chamber 16 is provided with aglow plug (not shown) connected to a battery (not shown) for temporarilycheating the glow plug.

The anvil 6 includes an anvil plate 22 arranged within the housing andan anvil shaft 25 fixedly connected to the anvil plate 22, the anvilshaft 25 extending through an opening provided in the housing 2 in amanner allowing the anvil 6 to move in longitudinal direction relativeto the housing 2 between a retracted position in which the pulser 1 hasa first volume and an extended position in which the pulser 1 has asecond volume larger than the first volume. A spring 28 biases the anvil6 to the retracted position thereof. The relative arrangement of theanvil 6 and the engine 4 is such that the anvil plate 22 is located ashort distance from the hammer 12 when both the engine 4 and the anvil 6are in their respective retracted positions.

Referring further to FIG. 2 there is shown an inlet valve 32 of theengine 4. The inlet valve 32 is in fluid communication with an oxygenreservoir 34 via a conduit 36 and with a hydrogen reservoir 38 via aconduit 40. The oxygen reservoir 34 contains a supply of oxygen at aselected pressure, and the hydrogen reservoir 38 contains a supply ofhydrogen at a selected pressure. The inlet valve 32 includes a valvebody 42 provided with a disc shaped chamber 44 having a valve seatsurface 46 provided with a first opening 48 in fluid communication withthe conduit 36, a second opening 50 in fluid communication with theconduit 40, and a third opening 52 in fluid communication with an inletopening (not shown) provided in the wall of the cylinder 8 via a conduit54. The position of the inlet opening is such that the piston 10 coversthe inlet opening during an initial stage of the combustion stroke, anduncovers the inlet opening during a final stage of the combustionstroke. A membrane 56 divides the disc shaped chamber 44 in a first zone60 in fluid communication with the respective openings 48, 50, 52 and asecond zone 62 in fluid communication with the combustion chamber 16 viaa conduit 64. The membrane 56 is flexible so as to allow the membrane tolay against the valve seat surface 46 if a fluid pressure in zone 62exceeds a fluid pressure in zone 60.

In FIG. 3 is an exhaust of the engine 4, which exhaust includes anoutlet opening 70 formed in the wall of the cylinder 8. For referencepurposes the piston 10 is shown together with the direction of movement71 of the piston 10 during a combustion stroke thereof. The position ofthe outlet opening 70 is such that the piston covers the outlet opening70 during an initial stage of the combustion stroke, and uncovers theoutlet opening 70 during a final stage of the combustion stroke. Theoutlet opening 70 is in fluid communication with an expansion chamber 72provided with a non-return valve 74 allowing combusted gas to flow fromthe expansion chamber 72 via the non-return valve 74 to the exterior ofthe engine 4 and preventing inflow of fluid from exterior the engine 4into the expansion chamber 72. The non-return valve 74 includes apassage 76 for combusted gas, which passage 76 is provided with a bodyof permeable material 78 including sintered steel.

During normal operation a stream of oxygen flows from the oxygenreservoir 34 via the conduit 36 into the first zone 60 of the chamber 44and a stream of hydrogen flows from the hydrogen reservoir 38 via theconduit 40 into the first zone 60. In said first zone the streams ofoxygen and hydrogen mix to form a stream of combustible gas mixturewhich flows via the conduit 54 into the combustion chamber 16. Ignitionof the gas mixture is achieved by inducing the battery to provide anelectric current to the glow plug. Upon ignition of the gas mixture, thepiston 10 performs a combustion stroke in the direction of arrow 71thereby compressing the spring 17 and moving the hammer 12 inlongitudinal direction towards the anvil plate 22. Continued movement ofthe hammer 12 causes the hammer 12 to impacts on the anvil plate 22thereby moving the anvil 6 from the retracted position to the extendedposition thereof. The piston 10 uncovers the inlet opening and theoutlet opening 70 during the final stage of the combustion stroke, thusallowing the combusted gas to flow via the outlet opening 70 into theexpansion chamber 72. The combusted gas expands in the expansion chamber72 and flows from there via the non-return valve 74 to the exterior ofthe power generator 1, thereby passing through the body of permeablematerial 78. The non-return valve 74 and the body of permeable material78 prevent fluid outside the power generator from entering the expansionchamber 72.

As the combusted gas flows out of the combustion chamber 16, thepressure in the combustion chamber drops to a level below the pressureof oxygen in the oxygen reservoir 34 and hydrogen in the hydrogenreservoir 38. As a result another stream of oxygen flows from the oxygenreservoir 34 via the conduit 36 into the first zone 60 of the chamber 44and a stream of hydrogen flows from the hydrogen reservoir 38 via theconduit 40 into the first zone 60. In said first zone the streams ofoxygen and hydrogen mix to form a fresh stream of combustible gasmixture which flows via the conduit 54 into the combustion chamber 16.

Upon completion of the combustion stroke, the spring 17 induces thepiston 10 to perform a compression stroke whereby the piston 10compresses the combustible gas mixture in the combustion chamber 17.During the compression stroke the pressure in the combustion chamber 16rises to a level above the selected pressure of oxygen and hydrogen inthe respective reservoirs 34, 38. Consequently the membrane 54 is biasedagainst the valve seat surface 46 thereby closing the openings 48, 50,52. Further inflow of combustible gas mixture into the combustionchamber 16 is thereby prevented. When the piston 10 arrives at the endof the compression stroke the pressure in the combustion chamber 17 isat a level causing the glow plug, which is still hot as a result of theprevious combustion cycle, to ignite the combustible gas mixture therebyinducing the piston 10 to perform another combustion stroke.

Simultaneously with the compression stroke of the piston 10, the spring28 biases the anvil 6 back to its retracted position.

The engine then automatically performs a sequence of combustion cycles,each combustion cycle including a compression stroke followed by acombustion stroke of the piston 10, as described above. The 12 hammerimpacts on the anvil plate 22 during each combustion stroke of thepiston 10, thereby causing a reciprocating movement of the anvilrelative to the housing 2. As a consequence the anvil shaft 25 causes asequence of pressure pulses in the wellbore fluid, which pressure pulsestravel to the pore fluid in the earth formation and prevent the pores ofthe formation from becoming clogged.

1. A pulser for generating pressure pulses in a wellbore formed in anearth formation to generate pressure pulses in said wellbore, the pulsercomprising a housing provided with an internal combustion engineincluding a cylinder and a piston arranged to perform a combustionstroke upon combustion of a combustible gas mixture in the cylinder, afirst spring arranged to induce the piston to perform a compressionstroke upon completion of the combustion stroke, the pulser furthercomprising a hammer connected to the piston, an anvil movable relativeto the housing between a first position and a second position in whichthe pulser has a different volume than in the first position, the anvilbeing arranged so that the hammer impacts against the anvil during thecombustion stroke and induces the anvil to move from the first to thesecond position, and a second spring biasing the anvil from the secondto the first position thereof.
 2. The pulser of claim 1, wherein theanvil extends through an opening provided in the housing to outside thehousing, and wherein in the second position of the anvil the length ofthe part of the anvil extending outside the housing is larger in thefirst position.
 3. The pulser of claim 1, wherein the engine is providedwith an inlet valve arranged to allow a stream of combustible gasmixture to enter the cylinder if the fluid pressure in the streamexceeds the fluid pressure in the cylinder.
 4. The pulser of claim 3,wherein the inlet valve comprises a valve body having a valve seatsurface provided with at least one opening for supplying the combustiblegas mixture to the combustion chamber, and a membrane arranged to covereach opening if the fluid pressure in the stream is lower than the fluidpressure in the cylinder.
 5. The pulser of claim 4, wherein the valveseat surface is provided with a first opening in fluid communicationwith an oxygen reservoir, a second opening in fluid communication with ahydrogen reservoir, and a third opening in fluid communication with thecombustion chamber, the membrane being arranged to cover the first,second and third openings if the fluid pressure in the stream is lessthan the fluid pressure in the cylinder.
 6. The power generator of claim1, wherein the engine is provided with an outlet for combusted gas, theoutlet including an outlet opening arranged in the wall of the cylinder,the outlet opening debouching into an expansion chamber provided with anon-return valve allowing combusted gas to flow from the expansionchamber via the non-return valve to the exterior of the engine andpreventing inflow of fluid from exterior the engine into the expansionchamber.
 7. The power generator of claim 6, wherein the expansionchamber is provided with a passage for combusted gas, the passage beingprovided with a body of permeable material.
 8. The power generator ofclaim 7, wherein the permeable material comprises sintered steel.